Re: [PATCH 1/3] grep: move grep_source_init outside critical section

[Jeff King <peff@peff.net>]

On Thu, Feb 15, 2018 at 10:56:13PM +0100, Rasmus Villemoes wrote:

> grep_source_init typically does three strdup()s, and in the threaded
> case, the call from add_work() happens while holding grep_mutex.
> 
> We can thus reduce the time we hold grep_mutex by moving the
> grep_source_init() call out of add_work(), and simply have add_work()
> copy the initialized structure to the available slot in the todo
> array.
> 
> This also simplifies the prototype of add_work(), since it no longer
> needs to duplicate all the parameters of grep_source_init(). In the
> callers of add_work(), we get to reduce the amount of code duplicated in
> the threaded and non-threaded cases slightly (avoiding repeating the
> "GREP_SOURCE_OID, pathbuf.buf, path, oid" argument list); a subsequent
> cleanup patch will make that even more so.

I think this makes sense. It does blur the memory ownership lines of the
grep_source, though. Can we make that more clear with a comment here:

> +	grep_source_init(&gs, GREP_SOURCE_OID, pathbuf.buf, path, oid);
> +
>  #ifndef NO_PTHREADS
>  	if (num_threads) {
> -		add_work(opt, GREP_SOURCE_OID, pathbuf.buf, path, oid);
> +		add_work(opt, &gs);
>  		strbuf_release(&pathbuf);
>  		return 0;
>  	} else

like:

  /* leak grep_source, whose fields are now owned by add_work() */

or something? We could even memset() it back to all-zeroes to avoid an
accidental call to grep_source_clear(), but that's probably unnecessary
if we have a comment.

-Peff